Dual mode communication systems and methods

ABSTRACT

Embodiments of dual mode communication systems and methods are disclosed. On system embodiment, among others, comprises logic configured to perform spatial multiplexing and expanded bandwidth signaling to data.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.11/105,909, filed Apr. 13, 2005, entitled “Dual Mode CommunicationSystems and Methods”, which claims priority to U.S. provisionalapplication No. 60/561,877, filed Apr. 14, 2004, all of which areentirely incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure is generally related to communication systems,and, more particularly, is related to wireless communication systems andmethods.

2. Related Art

Wireless communication systems are widely deployed to provide varioustypes of communication such as voice, data, and so on. These systems maybe based on code division multiple access (CDMA), time division multipleaccess (TDMA), orthogonal frequency division multiplex (OFDM), or someother multiplexing techniques. OFDM systems may provide high performancefor some channel environments. FIG. 1A is a block diagram thatillustrates an exemplary single-in, single-out (SISO) orthogonalfrequency division multiplexing (OFDM) communication system 100 (herein,SISO system 100) that is compliant with IEEE 802.11 standards. The SISOsystem 100 comprises a transmitter device 102 and a receiver device 104.The transmitter device 102 comprises a transmit (TX) processor 106,radio circuitry 108, and antenna 110. The receiver device 104 comprisesan antenna 112, radio circuitry 114, and receive (RX) processor 116.

The transmitter device 102 comprises well-known circuitry that dividesthe high-speed data signals into tens or hundreds of lower speed signalsand transmits the signals in parallel over respective frequencies withina radio frequency (RF) signal that comprise subcarrier frequencies(“subcarriers”). The frequency spectra of the sub-carriers overlap sothat the spacing between them is minimized. The subcarriers are alsoorthogonal to each other so that they are statistically independent anddo not create cross-talk or otherwise interfere with each other. Inoperation, the transmit processor 106 receives data signals (designatedas TX data1 at a defined data rate designated as TX Rate1). The transmitprocessor 106 encodes and interleaves the data and maps the interleaveddata into respective subcarrier channels as frequency domain symbols.Further processing by the transmit processor 106 may result in theinsertion of training signals, cyclic extensions (e.g., guardintervals), and additional processing such as inverse fast Fouriertransformations (IFFT) and wave shaping. The processed subcarriers areprovided to the radio circuitry 108, which provides filtering,modulation, amplification, and upconversion functionality, ultimatelyresulting in the transmission of data from antenna 110.

At the receiver device 104, the antenna 112 receives the transmitteddata, which is provided to radio circuitry 114 to complement theprocessing that occurred at radio circuitry 108. The data is thenprovided to receive (RX) processor 116, which provides clock recovery,cyclic extension removal, transformations (e.g., fast Fouriertransformation, FFT), demapping, deinterleaving, and decoding to recoverthe TX data1 as RX data1. Radio circuitry 108 and 114 comprisesynthesizers that operate at a single reference or carrier frequency(designated FREQ1).

FIG. 1B is a schematic diagram that illustrates spectrums of the signalsprocessed in the SISO system 100. In 802.11 standards, each OFDM symbol118 provided by the transmitter device 102 comprises 52 subcarriers(partially shown for brevity) centered at a defined reference or carrierfrequency (designated in FIGS. 1A and 1B as FREQ1), with a bandwidth(BW) of approximately 20 mega-Hertz (MHz). The spectrum 120 resultingfrom processing at the receiver device 104 is centered at the samereference or carrier frequency (FREQ1). Transmitter and receiver devicesthat implement OFDM processing pursuant to pre-proposed 802.11n standardare often referred to as legacy radios or legacy devices.

In terrestrial communication systems (e.g., a cellular system, abroadcast system, a multi-channel multi-point distribution system(MMDS), among others), a RF modulated signal from a transmitter devicemay reach a receiver device via a number of transmission paths. Thecharacteristics of the transmission paths typically vary over time dueto a number of factors such as fading and multi-path. To providediversity against deleterious path effects and improve performance,multiple transmit and receive antennas may be used for datatransmission. Spatial multiplexing refers to a technique where atransmission channel is divided into multiple “spatial channels” throughwhich independent streams can be transmitted and received via multipletransmit and receive antennas, respectively.

FIG. 2A is a block diagram that illustrates a multiple-inputmultiple-output (MIMO) OFDM communication system 200 (herein, MIMOsystem 200). The MIMO system 200 employs multiple transmit antennas andmultiple receive antennas for data transmission. Through spatialmultiplexing, a MIMO channel formed by the transmit and receive antennasmay be decomposed into independent channels. Each of the independentchannels is also referred to as a spatial subchannel of the MIMOchannel. The MIMO system 200 comprises a transmitter device 202 andreceiver device 204. The transmitter device 202 comprises transmit (TX)processors 206 and 212, radio circuitry 208 and 214, and antennas 210and 216. The radio circuitry 208 and 214 comprise synthesizers thatoperate at a single reference or carrier frequency (designated FREQ1).The receiver device 204 comprises antennas 218 and 226, radio circuitry220 and 228 (also comprising synthesizers that operate at a singlereference or carrier frequency, FREQ1), a signal separator 222 (e.g.,joint interference canceller), and receive (RX) processors 224 and 230.The transmit processors 206 and 212 and the radio circuitry 208 and 214comprise similar circuitry to that found in and described for transmitprocessor 106 (FIG. 1A), with the addition of circuitry for implementingspatial multiplexing. The radio circuitry 220 and 228 and receiveprocessors 224 and 230 also share common circuitry with like componentsshown in and described for receiver device 104 (FIG. 1A). The signalseparator 222 is configured to remove interference caused by multipletransmit signals occupying the same bandwidth at the receive antennas218 and 226, and thus are used to increase the data rate.

FIG. 2B is a schematic diagram that illustrates spectrums of the signalsprocessed in the MIMO system 200. As shown, the OFDM symbols 232 and 234are comprised of subcarriers centered at the same reference or carrierfrequency (FREQ1), each with a bandwidth (BW) of approximately 20 MHz.The spectrum 236 resulting from processing at the receiver device 204 iscentered at the same frequency (FREQ1).

Consumers continue to demand higher data rates. Current proposals to aproposed IEEE standard, 802.11n, are at least partially in response tothese demands. In the competitive communications industry, designers arechallenged to meet these new standards in cost effective ways.

SUMMARY

Embodiments of dual mode communication systems and methods aredisclosed. One system embodiment, among others, comprises logicconfigured to perform spatial multiplexing and expanded bandwidthsignaling to data.

One method embodiment, among others, comprises providing spatialmultiplexing and expanded bandwidth signaling for a plurality of data,and transmitting the plurality of data from a first transmit antenna anda second transmit antenna.

Other systems, methods, features, and advantages of the disclosedsystems and methods will be or become apparent to one with skill in theart upon examination of the following drawings and detailed description.It is intended that all such additional systems, methods, features, andadvantages be included within this description and be within the scopeof the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the disclosed systems and methods can be betterunderstood with reference to the following drawings. The components inthe drawings are not necessarily to scale, emphasis instead being placedupon clearly illustrating the principles of the disclosed systems andmethods. Moreover, in the drawings, like reference numerals designatecorresponding parts throughout the several views.

FIG. 1A is a block diagram that illustrates an exemplary single-in,single-out (SISO) orthogonal frequency division multiplexing (OFDM)communication system.

FIG. 1B is a schematic diagram that illustrates spectrums of the signalsprocessed in the SISO OFDM communication system shown in FIG. 1A.

FIG. 2A is a block diagram that illustrates a multiple-inputmultiple-output (MIMO) OFDM communication system.

FIG. 2B is a schematic diagram that illustrates spectrums of the signalsprocessed in the MIMO OFDM communication system shown in FIG. 2A.

FIG. 3A is a block diagram that illustrates an embodiment of a bandwidthexpansion and spatial multiplexing (BES) system.

FIG. 3B is a schematic diagram that illustrates an exemplary spectrum ofthe BES system shown in FIG. 3A.

FIGS. 3C-3D are schematic diagrams that illustrate exemplary adjacentand non-adjacent spectrums of the BES system shown in FIG. 3A.

FIG. 4 is a schematic diagram that illustrates fourth order spatialmultiplexing and first order expanded bandwidth as implemented by anembodiment of a BES system.

FIG. 5 is a schematic diagram that illustrates second order spatialmultiplexing and second order expanded bandwidth as implemented by anembodiment of a BES system.

FIG. 6 is a schematic diagram that illustrates first order spatialmultiplexing and fourth order expanded bandwidth as implemented by anembodiment of a BES system.

FIG. 7 is a flow diagram that illustrates a BES method embodiment.

DETAILED DESCRIPTION

Disclosed are various embodiments of bandwidth expansion and spatialmultiplexing systems and methods, herein referred to as a BES system.Such embodiments of the BES system comprise a dual-use or dual modearchitecture that provides for expanded bandwidth signaling that canalso be utilized for multiple-input, multiple output (MIMO) spatialmultiplexing. In other words, one embodiment of the BES system providesfor an architecture where the same or similar hardware is largely reusedfor MIMO spatial multiplexing and/or expanded bandwidth signaling. MIMOspatial multiplexing can be viewed as stacking multiple channels on topof each other in the frequency domain. Expanded bandwidth techniques canbe viewed as stacking multiple channels next to each other in thefrequency domain. Each signaling case (MIMO spatial multiplexing andexpanded bandwidth) can be viewed as duals of each other.

In this regard, the term “dual” refers to something that has a doublecharacter or nature. “Dualism” refers to a quality of state of having adual nature. In the disclosed embodiments, the dual nature of atransceiver is exploited by tuning to a defined frequency (spatialmultiplexing) or different frequency (bandwidth expansion). Suchtechniques can increase the data rate by spatial multiplexing (use ofmultiple transmit/receive chains with antennas in a multi-pathenvironment and a signal separator in the receiver device), whileenabling reuse of the same architecture as a bandwidth expansion radiodevice if the synthesizers of the respective transmit/receive chains aretuned to different, non-overlapping frequencies rather than the samefrequency. For example, on the receiver end, a signal separator isimplemented in spatial multiplexing, whereas in bandwidth expansion, asignal separator is not needed and the receive filters of a receiverdevice are tuned to the distinct frequencies. By providing the abilityto operate in either or both configurations using the same architecture,demand for increased data rates can be fulfilled using legacy radios ordevices in a cost effective manner.

Although described in the context of an OFDM system, it should beunderstood that embodiments of the BES system 300 may be implementedusing non-OFDM signaling methods, such as code division multiple access(CDMA), global system for mobile communications (GSM) in cellularcommunications, among other techniques and communication environments.

FIG. 3A is a block diagram that illustrates an embodiment of BES system300. The BES system 300 may also be referred to as a dual modecommunication system. In one embodiment, the BES system 300 comprises amultiple-input multiple-output (MIMO) orthogonal frequency divisionmultiplexing (OFDM) communication system that implements bandwidthexpansion and/or spatial multiplexing. The BES system 300 comprises atransmitter device 302 and a receiver device 304. The transmitter device302 may include functionality of the receiver device 304, and thereceiver device 304 may comprise functionality of the transmitter device302. Further, the transmitter device 302 and/or the receiver device 304may each be embodied in many wireless communication devices, includingcomputers (desktop, portable, laptop, etc.), consumer electronic devices(e.g., multi-media players), compatible telecommunication devices,personal digital assistants (PDAs), or any other type of networkdevices, such as printers, fax machines, scanners, hubs, switches,routers, set-top boxes, televisions with communication capability, etc.The transmitter device 302 comprises two modules 334 and 336. Module 334comprises a transmit (TX) processor 306, radio circuitry 310, antenna314, and synthesizer 342. Module 336 comprises a transmit (TX) processor308, radio circuitry 312, antenna 316, and synthesizer 344. Althoughsynthesizers 342 and 344 are shown separate from the radio circuitry 310and 312, in some embodiments, the synthesizers 342 and/or 344 may beincorporated into the radio circuitry 310 and 312, respectively, amongother locations.

Transmit processors 306 and 308 encode and interleave the incoming data(designated TX data1 and TX data2 at TX data rate1 and TX data rate2,respectively). Transmit processors 306 and 308 map the interleaved datainto respective subcarrier channels as frequency domain symbols, andinclude further processing for the insertion of training signals, cyclicextensions (e.g., guard intervals), and inverse fast Fouriertransformation (IFFT) and wave shaping. The processed subcarriers areprovided to the radio circuitry 310 and 312, which provides filtering,modulation, and amplification functionality. Radio circuitry 310 and 312receive reference or carrier frequency signals FREQ1 and FREQ2 fromsynthesizers 342 and 344, respectively, resulting in transmission ofsignals at distinct reference or carrier frequencies. By using separatereference or carrier frequencies, the transmitted signals can be easilyseparated by receive filters at the receiver device 304.

The receiver device 304 comprises modules 338 and 340. Module 338comprises an antenna 318, radio circuitry 322 comprising receive filter323 among other components, synthesizer 346, and receive (RX) processor326. The receive processor 326 comprises a signal separator 380. Module340 comprises an antenna 320, radio circuitry 324 comprising receivefilter 325 among other components, synthesizer 348, and receive (RX)processor 328. The receive processor 328 comprises a signal separator382. In some embodiments, other components may be used to separate thedata subcarriers of the signals. Although synthesizers 346 and 348 areshown separate from the radio circuitry 322 and 324, in someembodiments, the synthesizers 346 and/or 348 may be incorporated intothe radio circuitry 322 and 324, respectively. At the receiver device304, the antennas 318 and 320 receive the transmitted data, and providethe same to radio circuitry 322 and 324. The synthesizers 346 and 348provide downconversion functionality using reference or carrierfrequencies FREQ1 and FREQ2, respectively, which complements theprocessing that occurred at radio circuitry 310 and 312. In other words,the signals transmitted from antennas 314 and 316 are separated byfrequency at radio circuitry 322 and 324, respectively. With distinctfrequencies of operation (FREQ1 and FREQ2), the signal separators 380and 382 may be bypassed or disabled, since the receive filters 323 and325 are used to receive the separate carrier frequencies and rejectother channels. The corresponding downconverted signals are provided toreceive processors 326 and 328 to recover the original data as RX data1and RX data2. Receive processors 326 and 328 provide clock recovery,cyclic extension removal, transformation (e.g., fast Fouriertransformation, FFT), demapping, deinterleaving, and decodingfunctionality.

One or more components of the BES system 300 can be implemented usingdigital circuitry, analog circuitry, or a combination of both. Also, oneor more components of the BES system 300 can be implemented in hardware,software, firmware, or a combination thereof. If implemented inhardware, the one or more components of the BES system 300 can beimplemented with any or a combination of the following technologies,which are all well known in the art: a discrete logic circuit(s) havinglogic gates for implementing logic functions upon data signals, anapplication specific integrated circuit (ASIC) having appropriatecombinational logic gates, a programmable gate array(s) (PGA), a fieldprogrammable gate array (FPGA), etc.

If implemented partly or wholly in software, the one or more componentsof the BES system 300 can be comprised of software or firmware that isstored in a memory and that is executed by a suitable instructionexecution system.

FIG. 3B is a schematic diagram that illustrates exemplary spectrums forOFDM symbols of the BES system 300 shown in FIG. 3A. As shown, the OFDMsymbols 330 and 332 comprise subcarriers of equal bandwidth (BW) (e.g.,20 mega-Hertz (MHz) each), but at distinct reference or carrierfrequencies (FREQ1 and FREQ2) as opposed to the conventional mechanismsof using the same reference or carrier frequency.

FIGS. 3C-3D are schematic diagrams that illustrate exemplary adjacentand non-adjacent spectrums, respectively, of the BES system 300 shown inFIG. 3A. FIG. 3C illustrates adjacent spectrums 350 a and 350 b (orchannels) as generated during the processing of the received signals atthe receiver device 304 (FIG. 3A). FIG. 3D illustrates non-adjacentfrequency spectrums 352 a and 352 b (or channels) as generated duringthe processing of the received signals at the receiver device 304. Thebandwidth of such spectrums 352 a, 352 b can be much greater than, forexample, 20 MHz. Such an expanded bandwidth technique may provideseveral benefits, such as finding a free or available channel (sincethere is no requirement that the channels be adjacent). Further, inproposals to the proposed 802.11n standard, 40 MHz systems arecontemplated. In such an environment, it may be difficult to find acontiguous 40 MHz channel bandwidth. By providing the ability toimplement non-adjacent channels, the new proposed standard can beaccommodated as well.

Both frequency spectrums 350 a, 350 b and 352 a, 352 b revealnon-overlapping, non-interfering spectrums that result in a multi-foldincrease in the data rate (e.g., by using multiple 20 MHz channels, adoubling of the bandwidth can result in a two-fold increase in datarate). In other words, the BES system 300 (FIG. 3B) has increased thedata rate by transmitting the OFDM symbols side by side (separatechannels). Further, in this implementation, the operation of a signalseparators 380 and 382 is not needed (since by definition, signals atdistinct frequencies are separate). Also, by implementing expandedbandwidth techniques, the signaling overhead used to train a signalseparator can be eliminated.

FIGS. 4-6 illustrate the flexibility the embodiments of a BES system(similar to BES system 300, FIG. 3) can provide. Such differentconfigurations may be manually configured based upon a known user need,or automatically configured based upon operational conditions (e.g.,number of users, signal-to-noise ratio, multipath environment,interference, country where used, etc.). A media access controller (MAC,not shown) may determine the mode of operation (spatial, extendedbandwidth, combinations), or in some embodiments, the controllingapplication (e.g., multi-media player control processor) may control themode of operation. For example, FIG. 4 illustrates a frequency spectrum400 corresponding to a 4×4 MIMO spatial multiplexing BES systemoperating in a 20 MHz channel, implemented using fourth order spatialmultiplexing and first order expanded bandwidth. In other words, thedata rate is increase above the base rate (e.g., 20 MHz channels), andis achieved using only spatial multiplexing and no bandwidth expansion(e.g., greater than 20 MHz). In one embodiment, a BES system can beimplemented using 2×2 spatial multiplexing distributed across two 20 MHzchannels, as shown in FIG. 5 as a second order spatial multiplexing,second order expanded bandwidth spectrum 500. For the configurationsshown in FIGS. 4 and 5, the signal separators 380 and 382 (FIG. 3A) areoperational since multiple signals are occupying the same frequencychannel and thus self-interfering. For example, for the second orderspatial multiplexing configuration shown in FIG. 5, the signalseparators 380 and 382 separate two signals. For the fourth orderspatial multiplexing configuration shown in FIG. 4, the signalseparators 380 and 382 separate four signals. In one embodiment, a BESsystem can be implemented using first order spatial multiplexing andfourth order expanded bandwidth spectrum 600, as shown in FIG. 6. Insuch a configuration, the signal separators 380 and 382 need not beoperational, and thus training signals corresponding to the operation ofthe signal separators 380 and 382 can be bypassed.

Note that in some embodiments, gap filling may be provided between twospectrums with extra subcarriers, which may increase the composite datarate. For example, referring to FIG. 3C, subcarriers may fill in the gapbetween spectrums 350 a and 350 b.

Although described in the context of distinct synthesizers for eachrespective radio, in some embodiments, a single, adjustable synthesizermay be used for multiple transmit modules or multiple receiver modules.

As will be appreciated from the above description, one embodiment of aBES method 300 a is illustrated in FIG. 7. Any process descriptions orblocks in flow charts should be understood as representing modules,segments, or portions of code which include one or more executableinstructions for implementing specific logical functions or steps in theprocess, and alternate implementations are included within the scope ofthe preferred embodiment of the present invention in which functions maybe executed out of order from that shown or discussed, includingsubstantially concurrently or in reverse order, depending on thefunctionality involved, as would be understood by those reasonablyskilled in the art of the present invention.

As shown in FIG. 7, the BES method 300 a comprises providing spatialmultiplexing and expanded bandwidth signaling for a plurality of data(702), and transmitting the plurality of data from a first transmitantenna and a second transmit antenna (704). It should be emphasizedthat the above-described embodiments of the present disclosure,particularly, any “preferred” embodiments, are merely possible examplesof implementations, merely set forth for a clear understanding of theprinciples of the disclosed systems and methods. Many variations andmodifications may be made to the above-described embodiment(s) withoutdeparting substantially in scope. All such modifications and variationsare intended to be included herein within the scope of this disclosure.

1. A method comprising: selectively transmitting in a first mode and a second mode, wherein transmitting in the first mode comprises transmitting symbols from at least two transmitters in a MIMO spatial multiplexed mode by operating on separate data streams and generating separate transmit symbols for transmission in the same frequency band over separate antennas; and wherein transmitting in the second mode comprises transmitting symbols from at least two transmitters in a frequency division mode by operating on the separate data streams and generating separate transmit symbols for transmission in a plurality of non-overlapping frequency channels, wherein each frequency channel comprises a plurality of frequency subbands.
 2. The method of claim 1, wherein the at least two transmitters are configured to modulate and transmit symbols during the same period of time.
 3. The method of claim 1, wherein when transmitting in the first mode, each of the at least two transmitters are configured to modulate and to transmit symbols within the same frequency channel.
 4. The method of claim 1, wherein when transmitting in the second mode the at least two transmitters are configured to modulate and to transmit symbols in adjacent frequency channels.
 5. The method of claim 2, wherein when transmitting in the second mode the at least two transmitters are configured to modulate and to transmit symbols in non-adjacent frequency channels.
 6. A method comprising: selectively receiving in a first mode and a second mode, wherein receiving in the first mode comprises receiving symbols with at least two receivers in a MIMO spatial multiplexed mode by receiving data signals located in the same frequency band, and wherein both received data signals are received via at least two separate antennas; and wherein receiving in the second mode comprises receiving symbols with at least two receivers in a frequency division mode by receiving data signals located in non-overlapping frequency channels, wherein each frequency channel comprises a plurality of frequency subbands.
 7. The method of claim 6, wherein the at least two receivers are configured to modulate and transmit symbols during the same period of time.
 8. The method of claim 6, wherein when receiving in the first mode each of the at least two receivers are configured to jointly operate on separate received data signals located within the same frequency channel.
 9. The method of claim 6, wherein when receiving in the second mode the at least two receivers are configured to jointly operate on separate received data signals located in adjacent frequency channels.
 10. The method of claim 6, wherein when receiving in the second mode the at least two receivers are configured to jointly operate on separate received data signals located in non-adjacent frequency channels.
 11. An article of manufacture including a non-transitory computer-readable medium having instructions stored thereon that, upon execution by a computing device, cause the computing device to perform the operations comprising: selectively transmitting in a first mode and a second mode, wherein transmitting in the first mode comprises transmitting symbols from at least two transmitters in a MIMO spatial multiplexed mode by operating on separate data streams and generating separate transmit symbols for transmission in the same frequency band over separate antennas; and wherein transmitting in the second mode comprises transmitting symbols from at least two transmitters in a frequency division mode by operating on the separate data streams and generating separate transmit symbols for transmission in a plurality of non-overlapping frequency channels, wherein each frequency channel comprises a plurality of frequency subbands.
 12. The article of manufacture of claim 11, wherein the instructions, upon execution by a computing device, cause the computing device to perform the operation comprising transmitting symbols from the at least two transmitters during the same period of time.
 13. The article of manufacture of claim 11, wherein the instructions, upon execution by a computing device, cause the computing device to perform the operation comprising, when transmitting in the first mode, each of the at least two transmitters are configured to modulate and to transmit symbols within the same frequency channel.
 14. The article of manufacture of claim 11, wherein the instructions, upon execution by a computing device, cause the computing device to perform the operation comprising, when transmitting in the second mode, the at least two transmitters are configured to modulate and to transmit symbols in adjacent frequency channels.
 15. The article of manufacture of claim 11, wherein the instructions, upon execution by a computing device, cause the computing device to perform the operation comprising, when transmitting in the second mode, the at least two transmitters are configured to modulate and to transmit symbols in non-adjacent frequency channels.
 16. An article of manufacture including a non-transitory computer-readable medium having instructions stored thereon that, upon execution by a computing device, cause the computing device to perform the operations comprising: selectively receiving in a first mode and a second mode, wherein receiving in the first mode comprises receiving symbols with at least two receivers in a MIMO spatial multiplexed mode by receiving data signals located in the same frequency band, and wherein both received data signals are received via at least two separate antennas; and wherein receiving in the second mode comprises receiving symbols with at least two receivers in a frequency division mode by receiving data signals located in non-overlapping frequency channels, wherein each frequency channel comprises a plurality of frequency subbands.
 17. The article of manufacture of claim 16, wherein the instructions, upon execution by a computing device, cause the computing device to perform the operation comprising receiving symbols with the at least two receivers during the same period of time.
 18. The article of manufacture of claim 16, wherein the instructions, upon execution by a computing device, cause the computing device to perform the operation comprising, when receiving in the first mode, each of the at least two receivers are configured to jointly operate on separate received data signals located within the same frequency channel.
 19. The article of manufacture of claim 16, wherein the instructions, upon execution by a computing device, cause the computing device to perform the operation comprising, when receiving in the second mode, the at least two receivers are configured to jointly operate on separate received data signals located in adjacent frequency channels.
 20. The article of manufacture of claim 16, wherein the instructions, upon execution by a computing device, cause the computing device to perform the operation comprising, when receiving in the second mode, the at least two receivers are configured to jointly operate on separate received data signals located in non-adjacent frequency channels. 